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I wonder if the fsync patch will help with VM performance. Honestly the only things keeping me from using Btrfs as my main FS are 2 things:

1) I really don't understand how defragmentation works with Btrfs, with EXT4 I just forget about it, but I know that with Btrfs, because of COW, defragging will be important. And running the defrag command on the root directory will only defrag metadata not the contents (source: https://btrfs.wiki.kernel.org/index....doesn.27t_work) and running:

Code:

find -xdev -type f -exec btrfs fi defrag '{}' \;

seems really excessive

2) I do run VM's sometimes and from what I've heard and seen...Btrfs TANKS with VM's cuz its a lot of small writes.

Hole punching is a (very simple) compression method; it marks certain parts of a file as "unused", so that the filesystem knows that those parts don't have to be stored.

It represents the location of a file on the physical somewhat like this:

part 1 of the file: list of used disk sectors

part 2 of the file: marked as unused (this is the "hole" punched into the file)

part 3 of the file: list of used disk sectors

I'm not sure if file copying will be faster when using it (and it might depend on the software doing the copy supporting it), but theoretically it could be faster, especially if both source & destination filesystem support it.